Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$35.46	13.793%	$40.351	$40.35	$40.35	$40.40
Purchase #2	$57.41	10.634%	$63.515	$63.52	$63.50	$63.50
Purchase #3	$139.86	7.824%	$150.8026	$150.80	$150.80	$150.80
Purchase #4	$93.45	8.483%	$101.3774	$101.38	$101.40	$101.40
Purchase #5	$140.68	12.668%	$158.5013	$158.50	$158.50	$158.50
Purchase #6	$230.70	10.321%	$254.5105	$254.51	$254.50	$254.50
Purchase #7	$127.76	8.268%	$138.3232	$138.32	$138.30	$138.30
7 purchase totals =	$825.32		$907.3810	$907.38	$907.35	$907.40